Method and apparatus for fault-resilient multicast and unicast in transport networks

ABSTRACT

A capability is provided for supporting fault-resilient propagation of traffic in networks using redundant multicast trees (RMTs). Fault-resilient propagation of traffic from a first node to a second node is supported using one or both of a pair of RMTs rooted at the first node and a pair of RMTs rooted at the second node. The pair of RMTs rooted at the first node includes a pair of node-disjoint paths from the first node to the second node. The pair of RMTs rooted at the second node includes a pair of node-disjoint paths from the second node to the first node. The first node propagates multicast traffic toward the second node using at least one of the RMTs in the pair of RMTs rooted at the first node. The first node propagates unicast traffic toward the second node using at least one of: at least one of the RMTs in the pair of RMTs rooted at the first node, or at least one of the RMTs in the pair of RMTs rooted at the second node.

FIELD OF THE INVENTION

The invention relates to the field of transport networks and, morespecifically but not exclusively, to providing fault-resilientpropagation of traffic in transport networks.

BACKGROUND

As demand for multicast services continues to grow, service providerscontinue to seek low-cost, bandwidth-efficient, and fault-resilientmulticast transport capabilities for supporting the multicast services.In existing multicast transport networks, several different mechanismsare employed in an attempt to provide carrier-grade transport, at leastsome of which are based on the Ethernet technology known as ProviderBackbone Bridging-Traffic Engineered (PBB-TE). These mechanisms attemptto upgrade commonly-used Ethernet technology to meet rigorousrequirements of carrier-grade transport networks. More specifically,these mechanisms utilize independent spanning trees for each Virtual LAN(VLAN), where each VLAN spanning tree uniquely determines paths of thepackets belonging to the VLANs. Disadvantageously, however, use of suchmechanisms is inefficient and, thus, costly.

SUMMARY

Various deficiencies in the prior art are addressed by embodiments thatsupport fault-resilient propagation of multicast traffic and unicasttraffic using redundant multicast trees (RMTs).

In one embodiment, fault-resilient propagation of traffic from a firstnode to a second node is supported using one or both of a pair of RMTsrooted at the first node and a pair of RMTs rooted at the second node.The pair of RMTs rooted at the first node includes a pair ofnode-disjoint paths from the first node to the second node. The pair ofRMTs rooted at the second node includes a pair of node-disjoint pathsfrom the second node to the first node. The first node propagatesmulticast traffic toward the second node using at least one of the RMTsin the pair of RMTs rooted at the first node. The first node propagatesunicast traffic toward the second node using at least one of: at leastone of the RMTs in the pair of RMTs rooted at the first node, or atleast one of the RMTs in the pair of RMTs rooted at the second node.

BRIEF DESCRIPTION OF THE DRAWINGS

The teachings of the present invention can be readily understood byconsidering the following detailed description in conjunction with theaccompanying drawings, in which:

FIG. 1 depicts a high-level block diagram of a communication system;

FIG. 2 depicts the communication network of FIG. 1, illustrating a pairof RMTs for a first communication node of the communication network ofFIG. 1;

FIG. 3 depicts the communication network of FIG. 1, illustrating a pairof RMTs for a second communication node of the communication network ofFIG. 1;

FIG. 4 depicts a high-level block diagram of one embodiment of a methodfor configuring nodes of a transport network with RMT informationadapted for use in providing fault-resilient propagation of multicasttraffic and unicast traffic;

FIG. 5 depicts a high-level block diagram of one embodiment of a methodfor performing fault-resilient propagation of multicast traffic andunicast traffic from a source node using redundant multicast trees; and

FIG. 6 depicts a high-level block diagram of a general-purpose computersuitable for use in performing the functions described herein.

To facilitate understanding, identical reference numerals have beenused, where possible, to designate identical elements that are common tothe figures.

DETAILED DESCRIPTION OF THE INVENTION

A fault-resilient traffic propagation capability, adapted for use inproviding fault-resilient transport of multicast traffic and unicasttraffic in transport networks, is depicted and described herein. Thefault-resilient traffic propagation capability is primarily depicted anddescribed within the context of providing fault-resilient propagation ofmulticast traffic and unicast traffic within Ethernet-based transportnetworks, however, it will be appreciated by one skilled in the art andinformed by the teachings herein that the fault-resilient trafficpropagation capability depicted and described herein may be used toprovide fault-resilient transport of multicast and unicast traffic inother types of networks.

FIG. 1 depicts a high-level block diagram of a communication system. Asdepicted in FIG. 1, communication system 100 includes a communicationnetwork (CN) 110 and a management system (MS) 120. The CN 110 is a meshnetwork including a plurality of communication nodes (CNs) 112 ₁-112 ₈(collectively, CNs 112). The CNs 112 communicate using a plurality ofcommunication paths (CPs) 114.

The CNs 112 of CN 110 are transport nodes. In one embodiment, in whichCN 110 is an Ethernet-based transport network, CNs 112 are Ethernettransport nodes. In this embodiment, the CNs 112 each support Ethernetcapabilities, such as forwarding and bridging capabilities, as well asany other capabilities which may be supported by Ethernet-basedtransport nodes. The CNs 112 may be nodes associated with othertransport technologies.

The CPs 114 of CN 110 are communication paths, which may include directconnections between the CNs 112 and/or indirect connections between theCNs 112 (e.g., connections which may traverse other nodes). The CPs 114may be any type of communication paths adapted for supporting trafficfor CNs 112. The CPs 114 may support propagation of traffic using anyunderlying technologies suitable for supporting propagation of traffic.

Although depicted and described herein with respect to specific types,numbers, and topologies of communication nodes and communication paths(illustratively, the CNs 112 and CPs 114 of CN 110), it will beappreciated, by those skilled in the art and informed by the teachingsherein, that the fault-resilient traffic propagation capabilitiesdepicted and described herein may be utilized in transport networkshaving other types, numbers, and topologies of communication nodes andcommunication paths.

The MS 120 is a management system providing management functions for CN110. The management functions which may be provided by MS 120 aredescribed in detail hereinbelow. The MS 120 communicates with CN 110 viaa communication path (CP) 121. The MS 120 communicates with each of theCNs 112 of CN 110 via CP 121 and CPs 114 of CN 110. The MS 120 maycommunicate with the CNs 112 in any other suitable manner.

As described herein, redundant multicast trees (RMTs) are utilized tosupport fault-resilient transport of multicast traffic and unicasttraffic within a transport network (e.g., such as in the exemplarycommunication network, CN 110, of FIG. 1).

Two trees rooted at a source node r are termed RMTs if those two treesprovide two node-disjoint paths from source node r to every destinationnode in a set of destination nodes. Two trees termed RMTs may bereferred to as a pair of RMTs. A pair of RMTs computed for a target nodemay be said to include a first RMT and a second RMT, where the first RMTand second RMT provide a pair of node-disjoint paths from the targetnode to each of the other nodes associated with the pair of RMTs.

A node for which a pair of RMTs is computed is the root of the RMTs,and, thus, the pair of RMTs computed for the node are said to be rootedat that node. For a node having a pair of RMTs rooted thereat, under anysingle failure scenario (e.g., a failure of any single node, or afailure of any single link between nodes), the root node is able tocommunicate with every destination node using at least one of the twoRMTs in the pair of RMTs rooted at that node. The RMTs also may bereferred to as Protected Point-to-Multipoint (P2MP) trees.

A pair of RMTs rooted at a node may be computed using any suitablemethod for computing a pair of RMTs. In one embodiment, for example, thepair of RMTs computed for a node may be computed as described in“Redundant Trees for Preplanned Recovery in Arbitrary Vertex-Redundantor Edge-Redundant Graphs,” by Medard, Finn, Barry, and Gallager,IEEE/ACM Transactions on Networking, Vol. 7, No. 5, October 1999, whichis incorporated by reference herein in its entirety. In one embodiment,for example, the pair of RMTs computed for a node may be computed asdescribed in “Linear Time Construction of Redundant Trees for RecoverySchemes Enhancing QOP and QOS,” by Zhang, Xue, Tang, and Thulasiraman,INFOCOM 2005, 24th Annual Joint Conference of the IEEE Computer andCommunications Societies, Proceedings IEEE, Vol. 4, March 2005, which isincorporated by reference herein in its entirety. In one embodiment, forexample, the pair of RMTs computed for a node may be computed asdescribed in “The Multi-tree Approach to Reliability in DistributedNetworks,” by Itai and Rodeh, IEEE Symposium on Foundations of ComputerScience, 1984, which is incorporated by reference herein in itsentirety. In one embodiment, multiple such methods of computing a pairof RMTs for a node may be used together. The pair of RMTs for a node maybe computed using any other suitable method(s) for computing RMTs.

A pair of RMTs is computed for each of one or more nodes. The one ormore nodes may be a set of nodes, which may include any suitable scopeof nodes. For example, a set of nodes may include a subset of the nodesof a transport network, all of the nodes of a transport network, some orall of the nodes of each of multiple transport networks, and the like,as well as various combinations thereof. In other words, a pair of RMTscomputed for a source node r provides a pair of node-disjoint paths fromthe source node r to every destination node in a set of destinationnodes, where the set of destination nodes may include any suitablecombination of nodes to which traffic may be propagated from the sourcenode r using the pair of RMTs.

In one embodiment, in which pairs of RMTs are computed for respectivenodes of a set of nodes, the pairs of RMTs computed for nodes of a setof nodes are made uniquely identifiable for the set of nodes.

The pairs of RMTs may be made uniquely identifiable within the set ofnodes in any suitable manner.

In one embodiment, for example, the two RMTs computed for a node areeach assigned a respective identifier.

In one such embodiment, the identifiers assigned to the RMTs of a nodeinclude information which identifies that node. This will ensure thateach RMT identifier within the set of nodes is unique.

In another such embodiment, identifiers assigned to the RMTs of a nodemay be mapped to an identifier of that node. In this embodiment, the RMTidentifiers of a node must be unique for that node (and, optionally,each RMT identifier of the set of nodes may be unique, although this isnot required since the mapping of each node to its associated RMTidentifiers will provide unique identification of RMTs within the set ofnodes). In this embodiment, a combination of node identifier and RMTidentifier provide unique identification of RMTs within the set ofnodes.

The nodes of the set of nodes are each configured to include RMTinformation for each of the RMTs of the set of nodes. The RMTinformation provides an indication of each RMT pair rooted at eachrespective node of the set of nodes. In other words, for a given node ofa set of nodes, that given node is configured to be able to: (1)identify the RMT identifiers of the two RMTs rooted at that given node(i.e., RMTs rooted at itself) and (2) identify, for each other node ofthe set of nodes, the RMT identifiers of the two RMTs rooted at thatother node of the set of nodes. This ensures that a given node of theset of nodes is able to: (1) propagate multicast traffic, to each of theother nodes in the set of nodes, using the pair of RMTs rooted at thatgiven node (i.e., using the RMTs rooted at itself) and (2) propagateunicast traffic, to each other node in the set of nodes, using the pairof RMTs rooted at that given node or the pair of RMTs rooted at theother node to which the unicast traffic is to be propagated. Thepropagation of multicast traffic and unicast traffic using RMTs isdescribed in additional detail hereinbelow.

The RMT information may be specified using any suitable informationand/or in any suitable format. In one embodiment, for example, in whichidentifiers assigned to the RMTs of node identify that node, a list ofRMT identifiers for each of the RMTs computed for the set of nodes maybe provided to each of the nodes of the set of nodes. In one embodiment,for example, in which identifiers assigned to pairs of RMTs ofrespective nodes do not identify those nodes, a mapping table (includinga mapping of RMT identifiers to the nodes at which those RMTs arerooted, respectively) may be provided to each of the nodes of the set ofnodes. The RMT information may be specified using any other suitableinformation and/or in any other suitable format.

The nodes of the set of nodes may be configured to include the RMTinformation for each of the nodes of the set of nodes in any suitablemanner. In one embodiment, for example, the RMT information isdistributed to the nodes of the set of nodes by one or more managementsystems (e.g., by MS 120). In one embodiment, for example, the RMTinformation is exchanged between nodes of the set of nodes. The nodes ofthe set of nodes may be configured, to include the RMT information foreach of the nodes of the set of nodes, in any other suitable manner.

The computation of the RMT pairs for nodes of the set of nodes, and theconfiguring of nodes of the set of nodes with RMT information of thecomputed RMTs pairs, may be performed by one or more network elements ofthe communication network. In one embodiment, for example, suchfunctions are performed by one or more management systems (e.g., by MS120). In one embodiment, for example, such functions are performed byone or more of the transport nodes (e.g., where one or more of CNs 112is configured to perform such functions for CN 110). The aforementionedfunctions may be performed in any other suitable manner for computingRMT pairs for respective nodes and for configuring the respective nodeswith RMT information for the RMT pairs computed for the respectivenodes.

As described herein, following computation of RMT pairs for respectivenodes, and configuration of nodes with RMT information for the RMT pairscomputed for the respective nodes, the nodes use the computed RMTs forproviding fault-resilient propagation of multicast traffic and unicasttraffic between nodes of the set of nodes.

For multicast traffic to be propagated from a source node to multipledestination nodes, the multicast traffic is propagated using one or bothof the RMTs in the pair of RMTs rooted at the source node. The multicasttraffic is routed using the RMT identifier(s) of the RMT(s) on which themulticast traffic is propagated.

For unicast traffic to be propagated from a source node to a destinationnode, the unicast traffic is propagated using one of: (1) one or both ofthe RMTs in the pair of RMTs rooted at the source node, or (2) one orboth of the RMTs in the pair of RMTs rooted at the destination node. Ifthe unicast traffic is propagated using one or both of the RMTs in thepair of RMTs rooted at the source node, the unicast traffic is routedusing the RMT identifier(s) of the RMT(s) on which the unicast trafficis propagated, and an identifier of the destination node for which theunicast traffic is intended. If the unicast traffic is propagated usingone or both of the RMTs in the pair of RMTs rooted at the destinationnode, the unicast traffic is routed using the RMT identifier(s) of theRMT(s).

In the preceding description of fault-resilient propagation of multicasttraffic and unicast traffic using RMT(s), reference is made to using oneor both of the RMTs in a pair of RMTs to propagate traffic. This is toaccount for the different traffic protection schemes which may be usedwith the fault-resilient traffic propagation capabilities depicted anddescribed herein.

A first traffic protection scheme which may be used to protect multicasttraffic and/or unicast traffic is 1+1 protection. In a 1+1 trafficprotection scheme, traffic is propagated over both the active RMT andthe backup RMT of an RMT pair, such that the traffic may be selected atthe receiver from either the active RMT or the backup RMT.

A second traffic protection scheme which may be used to protectmulticast traffic and/or unicast traffic is 1:1 protection. In a 1:1traffic protection scheme, one RMT in the RMT pair is designated as anactive RMT and the other RMT in the RMT pair is designated as a backupRMT. In this traffic protection scheme, traffic is propagated over theactive RMT in the absence of a failure condition, and traffic ispropagated over both the active RMT and the backup RMT in the presenceof a failure condition.

The signaling of failure condition information in the transport networkmay be performed using any suitable method of signaling failurecondition information.

It will be appreciated that each node may use 1+1 protection and/or 1:1protection for multicast traffic and/or unicast traffic. For example,one of the two schemes may be used by all of the nodes of the network,one of the two schemes may be used by some nodes of the network whilethe other of the two schemes may be used by other nodes of the network,one or more nodes of the network may use both protection schemes (e.g.,using one scheme for unicast traffic and the other scheme for multicasttraffic, switching between the schemes on a session-by-session orpacket-by-packet basis independent of the type of traffic beingtransmitted, or using any other suitable combination of the schemes),and the like, as well as various combinations thereof. In other words,any node may use either or both of the two traffic protection schemes.

Although primarily depicted and described herein with respect to twotraffic protection schemes, it will be appreciated that one or moreother traffic protection schemes may be used, either in place of 1+1protection and/or 1:1 protection, or in addition to 1+1 protectionand/or 1:1 protection. Thus, it will be appreciated that any suitabletraffic protection schemes may be employed in combination with the RMTspairs depicted and described herein in order to provide fault-resilientpropagation of multicast and unicast traffic in transport networks.

The use of RMTs for propagating multicast traffic in transport networksmay be better understood by way of reference to the exemplary pair ofRMTs depicted and described herein with respect to FIG. 2. The use ofRMTs for propagating unicast traffic in transport networks may be betterunderstood by way of reference to the exemplary pairs of RMTs depictedand described herein with respect FIG. 2 and FIG. 3.

FIG. 2 depicts the communication network of FIG. 1, illustrating a pairof RMTs for a first communication node of the communication network ofFIG. 1. As depicted in FIG. 2, a pair of RMTs 201 is computed for CN 112₁. The pair of RMTs 201 rooted at CN 112 ₁ includes a first RMT 201 ₁and a second RMT 201 ₂.

The first RMT 201 ₁ includes the following paths: from CN 112 ₁ to CN112 ₂, from CN 112 ₂ to CN 112 ₅, from CN 112 ₅ to CN 112 ₈, from CN 112₁ to CN 112 ₄, from CN 112 ₄ to CN 112 ₃, from CN 112 ₄ to CN 112 ₆, andfrom CN 112 ₄ to CN 112 ₇. Thus, every CN 112 ₂-112 ₈ is reachable fromroot CN 112 ₁ via first RMT 201 ₁.

The second RMT 201 ₂ includes the following paths: from CN 112 ₁ to CN112 ₃, from CN 112 ₃ to CN 112 ₅, from CN 112 ₅ to CN 112 ₂, from CN 112₃ to CN 112 ₄, from CN 112 ₃ to CN 112 ₆, from CN 112 ₆ to CN 112 ₇, andfrom CN 112 ₆ to CN 112 ₈. Thus, every CN 112 ₂-112 ₈ is reachable fromroot CN 112 ₁ via second RMT 201 ₂.

The first RMT 201 ₁ and second RMT 201 ₂ provide two node-disjoint pathsfrom root node CN 112 ₁ to every other node, CN 112 ₂-CN 112 ₈, in CN110. For example, the path from CN 112 ₁ to CN 112 ₈ on first RMT 201 ₁follows the path CN 112 ₁→CN 112 ₂→CN 112 ₅→CN 112 ₈, and the path fromCN 112 ₁ to CN 112 ₈ on second RMT 201 ₂ follows the path CN 112 ₁→CN112 ₃→CN 112 ₆→CN 112 ₈. The paths from CN 112 ₁ to CN 112 ₈ on firstRMT 201 ₁ and second RMT 201 ₂ do not share any links or nodes betweenCN 112 ₁ and CN 112 ₈, and, thus, are disjoint. This holds true forpaths from root CN 112 ₁ to every other communication node in CN 110(i.e., for CNs 112 ₂-112 ₇).

As described herein, where root CN 112 ₁ is operating as a source ofmulticast traffic to be delivered to each of the other CNs 112, one orboth of the first RMT 201 ₁ and the second RMT 201 ₂ computed for androoted at CN 112 ₁ may be used to propagate multicast traffic from rootnode CN 112 ₁ to each of the other CNs 112.

If 1+1 protection is used for the multicast traffic, the CN 112 ₁transmits the multicast traffic on both the first RMT 201 ₁ and thesecond RMT 201 ₂, and each of the receivers of the multicast traffic canreceive the multicast traffic on the active RMT or the backup RMT (i.e.,either first RMT 201 ₁ or second RMT 201 ₂, depending on whether thereis a failure condition in the network).

If 1:1 protection is used for the multicast traffic, CN 112 ₁ initiallyonly transmits the multicast traffic on an active RMT (i.e., eitherfirst RMT 201 ₁ or second RMT 201 ₂, depending on which one is active).If there is a failure condition in the network, the root CN 112 ₁ beginstransmitting the multicast traffic on both the active RMT and the backupRMT (i.e., on both first RMT 201 ₁ and second RMT 201 ₂) until thefailure condition is resolved.

Although omitted from FIG. 2 for purposes of clarity, one or more pairsof RMTs also may be computed for one or more other CNs 112 of thecommunication network, respectively.

As described hereinabove, the pair of RMTs 201 computed for CN 112 ₁also may be used for propagating unicast traffic from CN 112 ₁ toindividual ones of the other CNs 112. The unicast traffic may bepropagated using the pair of RMTs 201 computed for CN 112 ₁ using 1+1and/or 1:1 protection. As described hereinabove, however, the pair ofRMTs 201 computed for CN 112 ₁ is not the only pair of RMTs availablefor use by the CN 112, for propagating unicast traffic from CN 112 ₁;rather, for unicast traffic to be propagated from CN 112 ₁ to one of theother CNs 112, the pair of RMTs that is rooted at the other one of theCNs 112 for which the unicast traffic is intended also may be used topropagate the unicast traffic). This capability is depicted anddescribed in more detail with respect to FIG. 3.

FIG. 3 depicts the communication network of FIG. 1, illustrating a pairof RMTs for a second communication node of the communication network ofFIG. 1. As depicted in FIG. 3, a pair of RMTs 301 is computed for CN 112₈. The pair of RMTs 301 rooted at CN 112 ₈ includes a first RMT 301 ₁and a second RMT 301 ₂.

The first RMT 301 ₁ includes the following paths: from CN 112 ₈ to CN112 ₇, from CN 112 ₇ to CN 112 ₆, from CN 112 ₇ to CN 112 ₄, from CN 112₄ to CN 112 ₁, from CN 112 ₈ to CN 112 ₅, from CN 112 ₅ to CN 112 ₂, andfrom CN 112 ₂ to CN 112 ₃. Thus, every CN 112 ₁-112 ₇ is reachable fromroot CN 112 ₈ via first RMT 301 ₁.

The second RMT 301 ₂ includes the following paths: from CN 112 ₈ to CN112 ₆, from CN 112 ₆ to CN 112 ₇, from CN 112 ₆ to CN 112 ₅, from CN 112₆ to CN 112 ₃, from CN 112 ₃ to CN 112 ₄, from CN 112 ₃ to CN 112 ₂, andfrom CN 112 ₂ to CN 112 ₁. Thus, every CN 112 ₁-112 ₇ is reachable fromroot CN 112 ₈ via second RMT 301 ₂.

The first RMT 301 ₁ and second RMT 301 ₂ provide two disjoint paths fromroot node CN 112 ₈ to every other node, CN 112 ₁-CN 112 ₇, in CN 110.

As described herein, where CN 112 ₁ (source node) is operating as asource of unicast traffic to be delivered to CN 112 ₈ (destinationnode), the unicast traffic may be propagated from CN 112 ₁ to CN 112 ₈using either: (1) one or both of first RMT 201 ₁ and second RMT 201 ₂rooted at source node CN 112 ₁ (as depicted in FIG. 2), or (2) one orboth of first RMT 301 ₁ and second RMT 301 ₂ rooted at destination nodeCN 112 ₈ (as depicted in FIG. 3). If unicast traffic is propagated usingfirst RMT 201 ₁ rooted at CN 112 ₁, the traffic follows a path from CN112 ₁→CN 112 ₂→CN 112 ₅→CN 112 ₈. If unicast traffic is propagated usingsecond RMT 201 ₂ rooted at CN 112 ₁, the traffic follows a path from CN112 ₁→CN 112 ₃→CN 112 ₆→CN 112 ₈. If unicast traffic is propagated usingfirst RMT 301 ₁ rooted at CN 112 ₈, the traffic follows a path from CN112 ₁→CN 112 ₄→CN 112 ₇→CN 112 ₈. If unicast traffic is propagated usingsecond RMT 301 ₂ rooted at CN 112 ₈, the traffic follows a path from CN112 ₁→CN 112 ₂→CN 112 ₃→CN 112 ₆→CN 112 ₈.

If 1+1 protection is used for the unicast traffic, the CN 112 ₁transmits the unicast traffic using: (1) the first RMT 201 ₁ and thesecond RMT 201 ₂ rooted at CN 112 ₁, or (2) the first RMT 301 ₁ and thesecond RMT 301 ₂ rooted at CN 112 ₈. As with the multicast traffic, thedestination node of the unicast traffic can receive the unicast trafficon the active RMT or the backup RMT of the pair of RMTs used topropagate the unicast traffic.

If 1:1 protection is used for the unicast traffic, CN 112 ₁ transmitsthe unicast traffic using: (1) either first RMT 201 ₁ or second RMT 201₂ (depending on which one is active) in the absence of a failurecondition, and using both first RMT 201 ₁ and second RMT 201 ₂ in thepresence of a failure condition until the failure condition is resolved;or (2) either first RMT 301 ₁ or second RMT 301 ₂ (depending on whichone is active) in the absence of a failure condition, and using bothfirst RMT 301 ₁ and second RMT 301 ₂ in the presence of a failurecondition until the failure condition is resolved.

Although omitted from FIG. 3 for purposes of clarity, one or more pairsof RMTs also may be computed for one or more other CNs 112 of thecommunication network, respectively.

In one embodiment, in which the fault-resilient traffic propagationcapability depicted and described herein is implemented in anEthernet-based transport network, a source node may prefer to or beconfigured to propagate unicast traffic toward a destination node usingthe RMT(s) rooted at the destination node (rather than using the RMT(s)rooted at the source node) when an address learning mechanism isavailable in the Ethernet-based transport network. The nodes of theEthernet-based transport network may be configured to always propagateunicast traffic using the RMT(s) of the destination node where it isknown a priori that an address learning mechanism is available in theEthernet-based transport network. Alternatively, if the nodes of theEthernet-based transport network are unsure as to whether an addresslearning mechanism is available in the Ethernet-based transport network,the nodes may determine whether or not an address learning mechanism isavailable before deciding whether to use the RMT(s) rooted at the sourcenode or the RMT(s) rooted at the destination node.

FIG. 4 depicts one embodiment of a method for configuring a set of nodeswith RMT information adapted for use in providing fault-resilientpropagation of multicast traffic and unicast traffic. Although primarilydepicted and described herein as being performed serially, at least aportion of the steps of method 400 may be performed contemporaneously,or in a different order than depicted and described with respect to FIG.4.

As depicted in FIG. 4, the method 400 begins at step 402. At step 404, apair of RMTs is computed for each node of the set of nodes. At step 406,RMT information associated with the pairs of RMTs is propagated to eachnode of the set of nodes. At step 408, the method 400 ends. The steps ofmethod 400 may be better understood by way of reference to FIG. 1, adescription of which is provided hereinabove.

FIG. 5 depicts one embodiment of a method for performing fault-resilientpropagation of multicast traffic and unicast traffic from a source nodeusing redundant multicast trees. Although primarily depicted anddescribed herein as being performed serially, at least a portion of thesteps of method 500 may be performed contemporaneously, or in adifferent order than depicted and described with respect to FIG. 5.

As depicted in FIG. 5, the method 500 begins at step 502. At step 504,multicast traffic is propagated from the source node toward one or moredestination nodes using one or both of the RMTs in a pair of RMTs rootedat the source node. At step 506, unicast traffic is propagated from thesource node toward a destination node using one or both of the RMTs in apair of RMTs rooted at the source node or using one or both of the RMTsin a pair of RMTs rooted at the destination node. At step 508, method500 ends.

The steps of the method 500 may be better understood by way of referenceto FIGS. 1-3, descriptions of which are provided hereinabove.

It will be appreciated that when considering propagation of multicasttraffic and unicast traffic from a source node to a particulardestination node, the source node and destination node may be referredto more generally as a first node and a second node, respectively.

It will be appreciated that references made herein to source node anddestination node are primarily made for purposes of explainingpropagation of traffic between nodes, and is not intended to limit thecapabilities of the nodes to which reference is made. In this manner,labeling of a node as a source node does not preclude the capability ofthat node to operate as a destination node for traffic originating atanother node and, similarly, labeling of a node as a destination nodedoes not preclude the capability of that node to operate as a sourcenode for providing traffic to one or more other nodes.

As described herein, the fault-resilient traffic propagationcapabilities depicted and described herein may be used in order toprovide fault-resilient protection of multicast traffic and unicasttraffic in Ethernet-based transport networks. The fault-resilienttraffic propagation capabilities depicted and described herein arecompatible with existing Ethernet forwarding/bridging mechanismsspecified by the Ethernet standards. The fault-resilient trafficpropagation capabilities depicted and described herein also arecompatible with the emerging Institute of Electrical and ElectronicsEngineers (IEEE) 802.1aq Standard.

Although depicted and described herein with respect to embodiments inwhich a pair of RMTs is computed and established for each node of atransport network, respectively, it will be appreciated that pairs ofRMTs may be computed and established for respective nodes of a subset ofnodes of the transport network, respective nodes of multiple transportnetworks, and the like, as well as various combinations thereof.

FIG. 6 depicts a high-level block diagram of a general-purpose computersuitable for use in performing the functions described herein. Asdepicted in FIG. 6, system 600 comprises a processor element 602 (e.g.,a CPU), a memory 604, e.g., random access memory (RAM) and/or read onlymemory (ROM), an RMT management module 605, and various input/outputdevices 606 (e.g., storage devices, including but not limited to, a tapedrive, a floppy drive, a hard disk drive or a compact disk drive, areceiver, a transmitter, a speaker, a display, an output port, and auser input device (such as a keyboard, a keypad, a mouse, and thelike)).

It should be noted that the present invention may be implemented insoftware and/or in a combination of software and hardware, e.g., usingapplication specific integrated circuits (ASIC), a general purposecomputer or any other hardware equivalents. In one embodiment, the RMTmanagement process 605 can be loaded into memory 604 and executed byprocessor 602 to implement the functions as discussed above. As such RMTmanagement process 605 (including associated data structures) of thepresent invention can be stored on a computer readable medium orcarrier, e.g., RAM memory, magnetic or optical drive or diskette, andthe like.

It is contemplated that some of the steps discussed herein as softwaremethods may be implemented within hardware, for example, as circuitrythat cooperates with the processor to perform various method steps.Portions of the functions/elements described herein may be implementedas a computer program product wherein computer instructions, whenprocessed by a computer, adapt the operation of the computer such thatthe methods and/or techniques described herein are invoked or otherwiseprovided. Instructions for invoking the inventive methods may be storedin fixed or removable media, transmitted via a data stream in abroadcast or other signal bearing medium, and/or stored within a memorywithin a computing device operating according to the instructions.

Although various embodiments which incorporate the teachings of thepresent invention have been shown and described in detail herein, thoseskilled in the art can readily devise many other varied embodiments thatstill incorporate these teachings.

What is claimed is:
 1. A method for providing fault-resilientpropagation of traffic from a first node toward a second node, whereinthe first node and the second node each have a respective pair ofredundant multicast trees (RMTs) rooted thereat, wherein the pair ofRMTs rooted at the first node comprises a pair of node-disjoint pathsfrom the first node to the second node and the pair of RMTs rooted atthe second node comprises a pair of node-disjoint paths from the secondnode to the first node, the method comprising: propagating multicasttraffic from the first node toward the second node using at least one ofthe RMTs in the pair of RMTs rooted at the first node; and propagatingunicast traffic from the first node toward the second node using atleast one of the RMTs in the pair of RMTs rooted at the first node, orat least one of the RMTs in the pair of RMTs rooted at the second node.2. The method of claim 1, wherein the unicast traffic is propagated fromthe first node toward the second node using at least one of the RMTs inthe pair of RMTs rooted at the second node when the second node supportsan address learning mechanism.
 3. The method of claim 1, wherein: when a1+1 protection scheme is used, the multicast traffic is propagated usingboth of the RMTs in the pair of RMTs rooted at the first node; and whena 1:1 protection scheme is used, the multicast traffic is propagatedusing one of the RMTs in the pair of RMTs rooted at the first node inthe absence of a failure condition and is propagated using both of theRMTs in the pair of RMTs rooted at the first node in the presence of afailure condition.
 4. The method of claim 1, wherein: when a 1+1protection scheme is used, the unicast traffic is propagated using oneof: both of the RMTs in the pair of RMTs rooted at the first node orboth of the RMTs in the pair of RMTs rooted at the second node; and whena 1:1 protection scheme is used, the unicast traffic is propagated usingone of: one of the RMTs in the pair of RMTs rooted at the first node inthe absence of a failure condition, or both of the RMTs in the pair ofRMTs rooted at the first node in the presence of a failure condition; orone of the RMTs in the pair of RMTs rooted at the second node in theabsence of a failure condition, or both of the RMTs in the pair of RMTsrooted at the second node in the presence of a failure condition.
 5. Themethod of claim 1, further comprising: receiving, at the first node, apair of RMT identifiers associated with the pair of RMTs rooted at thesecond node.
 6. The method of claim 1, wherein the first and secondnodes form part of an Ethernet-based transport network.
 7. A first nodefor providing fault-resilient propagation of traffic node toward asecond node, wherein the first node and the second node each have arespective pair of redundant multicast trees (RMTs) rooted thereat,wherein the pair of RMTs rooted at the first node comprises a pair ofnode-disjoint paths from the first node to the second node and the pairof RMTs rooted at the second node comprises a pair of node-disjointpaths from the second node to the first node, wherein the first nodecomprises: means for propagating multicast traffic toward the secondnode using at least one of the RMTs in the pair of RMTs rooted at thefirst node; and means for propagating unicast traffic toward the secondnode using at least one of: at least one of the RMTs in the pair of RMTsrooted at the first node, or at least one of the RMTs in the pair ofRMTs rooted at the second node.
 8. The node of claim 7, wherein theunicast traffic is propagated toward the second node using at least oneof the RMTs in the pair of RMTs rooted at the second node when thesecond node supports an address learning mechanism.
 9. The apparatus ofclaim 7, wherein: when a 1+1 protection scheme is used, the multicasttraffic is propagated using both of the RMTs in the pair of RMTs rootedat the first node; and when a 1:1 protection scheme is used, themulticast traffic is propagated using one of the RMTs in the pair ofRMTs rooted at the first node in the absence of a failure condition andis propagated using both of the RMTs in the pair of RMTs rooted at thefirst node in the presence of a failure condition.
 10. The apparatus ofclaim 7, wherein: when a 1+1 protection scheme is used, the unicasttraffic is propagated using one of: both of the RMTs in the pair of RMTsrooted at the first node or both of the RMTs in the pair of RMTs rootedat the second node; and when a 1:1 protection scheme is used, theunicast traffic is propagated using one of: one of the RMTs in the pairof RMTs rooted at the first node in the absence of a failure condition,or both of the RMTs in the pair of RMTs rooted at the first node in thepresence of a failure condition; or one of the RMTs in the pair of RMTsrooted at the second node in the absence of a failure condition, or bothof the RMTs in the pair of RMTs rooted at the second node in thepresence of a failure condition.
 11. The apparatus of claim 7, furthercomprising: means for receiving a pair of RMT identifiers associatedwith the pair of RMTs rooted at the second node.
 12. The apparatus ofclaim 7, the first node forms part of an Ethernet-based transportnetwork.
 13. A non-transitory computer readable storage medium storing asoftware program which, when executed by a computer, causes the computerto perform a method for providing fault-resilient propagation of trafficfrom a first node toward a second node, wherein the first node and thesecond node each have a respective pair of redundant multicast trees(RMTs) rooted thereat, wherein the pair of RMTs rooted at the first nodecomprises a pair of node-disjoint paths from the first node to thesecond node and the pair of RMTs rooted at the second node comprises apair of node-disjoint paths from the second node to the first node, themethod comprising: propagating multicast traffic from the first nodetoward the second node using at least one of the RMTs in the pair ofRMTs rooted at the first node; and propagating unicast traffic from thefirst node toward the second node using at least one of: at least one ofthe RMTs in the pair of RMTs rooted at the first node, or at least oneof the RMTs in the pair of RMTs rooted at the second node.
 14. Thenon-transitory computer readable storage medium of claim 13, wherein theunicast traffic is propagated from the first node toward the second nodeusing at least one of the RMTs in the pair of RMTs rooted at the secondnode when the second node supports an address learning mechanism. 15.The non-transitory computer readable storage medium of claim 13,wherein: when a 1+1 protection scheme is used, the multicast traffic ispropagated using both of the RMTs in the pair of RMTs rooted at thefirst node; and when a 1:1 protection scheme is used, the multicasttraffic is propagated using one of the RMTs in the pair of RMTs rootedat the first node in the absence of a failure condition and ispropagated using both of the RMTs in the pair of RMTs rooted at thefirst node in the presence of a failure condition.
 16. Thenon-transitory computer readable storage medium of claim 13, wherein:when a 1+1 protection scheme is used, the unicast traffic is propagatedusing one of: both of the RMTs in the pair of RMTs rooted at the firstnode or both of the RMTs in the pair of RMTs rooted at the second node;and when a 1:1 protection scheme is used, the unicast traffic ispropagated using one of: one of the RMTs in the pair of RMTs rooted atthe first node in the absence of a failure condition, or both of theRMTs in the pair of RMTs rooted at the first node in the presence of afailure condition; or one of the RMTs in the pair of RMTs rooted at thesecond node in the absence of a failure condition, or both of the RMTsin the pair of RMTs rooted at the second node in the presence of afailure condition.
 17. The non-transitory computer readable storagemedium of claim 13, further comprising: receiving, at the first node, apair of RMT identifiers associated with the pair of RMTs rooted at thesecond node.
 18. The non-transitory computer readable storage medium ofclaim 13, wherein the first and second nodes form part of anEthernet-based transport network.
 19. A method for enablingfault-resilient propagation of multicast traffic and unicast trafficfrom a first node toward a second node, comprising: computing, for thefirst node, a pair of redundant multicast trees (RMTs) rooted at thefirst node, wherein the pair of RMTs rooted at a first node comprises apair of node-disjoint paths from the first node to the second node;computing, for the second node, a pair of redundant multicast trees(RMTs) rooted at the second node, wherein the pair of RMTs rooted at thesecond node comprises a pair of node-disjoint paths from the second nodeto the first node; and propagating, toward the first node, RMTinformation associated with the pairs of RMTs computed for first andsecond nodes, wherein the RMT information is adapted for use by thefirst node to provide fault-resilient propagation of traffic toward thesecond node by: propagating multicast traffic from the first node towardthe second node using at least one of the RMTs in the pair of RMTsrooted at the first node; and propagating unicast traffic from the firstnode toward the second node using at least one of: at least one of theRMTs in the pair of RMTs rooted at the first node, or at least one ofthe RMTs in the pair of RMTs rooted at the second node.
 20. A system forproviding fault-resilient propagation of multicast traffic and unicasttraffic using redundant multicast trees, comprising a plurality of nodesfor transmitting and receiving multicast traffic and unicast traffic;and a management system, for computing, for each of the nodes, a pair ofRMTs rooted at that node, and for propagating, to each of the nodes, RMTinformation associated with the pairs of RMTs computed for therespective nodes; wherein the RMT information propagated to the nodes isadapted for use by the nodes to perform fault-resilient propagation ofmulticast traffic and unicast traffic; wherein propagation of multicasttraffic from a first node comprises propagating the multicast trafficusing at least one of the RMTs in the pair of RMTs rooted at the firstnode; wherein propagation of unicast traffic from a first node toward asecond node comprises propagating the unicast traffic using at least oneof: at least one of the RMTs in the pair of RMTs rooted at the firstnode, or at least one of the RMTs in the pair of RMTs rooted at thesecond node.